Something I’ve been trying to figure out for a while is a way to have spine IK which allows animating the position of the head directly, and just moves the body to follow. That seems useful in general, so you can animate dialogue head movement precisely without having to fight spine IK. A good “stress test” example is sipping from a glass or straw on a table while sitting (everyone’s poured a carbonated drink too fast). That’s an easy, intuitive movement that anyone can do, bending your back so your head goes exactly where you want it (the glass), while your hip stays planted on the chair.
So far I haven’t found a good spline IK setup for this. Typical spine setups are hip-anchored: the hip stays in place, and the head just lands somewhere along an IK curve. I tried reversing the chain: create a joint hierarchy starting at the head and going down to the spine, and setting up spline IK that way. That just inverts the problem: the head goes to the right place, but the hip moves around instead of staying in place.
Of course, a regular single chain IK will reach the start and end points, but we want a spine bend, not an elbow.
(The right approach might actually be anchored at the neck or upper spine rather than the head, since it’s a simpler curve and would give better control over head rotation, but that’s a detail for later.)
It’s really intuitively obvious what should happen, and it feels like this should be an easy variation of a standard IK setup, but for some reason I’m having trouble with it. Anyone have any ideas?
